The present invention relates to an integrated circuit, and more particularly to a diode.
Integrated circuit devices contain many regions of doped semiconductor material. These doped regions may be either positively doped (p-type) so that they have an excess of holes, or they may be negatively doped (n-type) so that they have an excess of electrons. The boundary of positively doped and negatively doped regions creates a pn junction, which is the foundation for much of the semiconductor industry.
In non-ideal semiconductor devices, there are numerous regions of intersecting p-type and n-type material. As a result, unintended pn junctions. npn transistors and pnp transistors may be formed in addition to junctions intended to be created in the semiconductor device. These unintentional junctions and transistors, which are often oriented perpendicular to the substrate, can draw current away from its intended path. The current that is unintentionally drawn away from its intended path is referred to as “parasitic” current.
Parasitic current causes two main problems in semiconductor devices. First, parasitic current reduces the efficiency of the device by drawing current away from its intended path. Second, parasitic current may reach the doped substrate region of the device. Once in the substrate, the parasitic current is conducted to other parts of the device, where it may affect the current flow in other regions of the semiconductor device. Particularly, parasitic current can cause the problem of “latchup” in a semiconductor device. Latchup occurs when the parasitic current unintentionally drives a transistor into saturation mode. The saturation is sustained by positive feedback, which can prevent the circuit from operating and can also cause permanent damage and burn-out of the circuit.
One known method of reducing parasitic current is to electrically isolate semiconductor devices located on the same chip from one another. One known type of isolation is trench isolation. Using this technique, trenches are dug into the substrate around the various semiconductor devices on the chip. These trenches are typically dug using molecular beam epitaxy or ion bombardment. After the trench is dug, an oxide is grown inside of the trench. The oxide is an insulator and thus electrically isolates the device from other devices on the same chip. However, trench isolation is expensive and increases the number of steps that are needed to make a semiconductor device.